Point-to-multipoint communication systems provide service to a large number of subscribers or remote stations from a central base station (or central base station) at each node. To maximize the number of subscribers serviced by the base station, the node may be sectorized into several sectors with a separate transceiver (transmitter and receiver) and antenna system for each sector. This provides for 100% frequency reuse on each sector. The polarization of transmitted and received signal may alternate about the node as disclosed in J. Leland Langston application Ser. No. 08/345,183, filed Nov. 28, 1994 entitled "Low Power, Short Range Point-to-Multipoint Communications System" incorporated herein by reference. This provides for 100% frequency reuse but creates sector to sector interference possibilities.
Previous 2-way point-to-multipoint systems include cellular telephony systems, wireless local loop systems, and satellite communication systems. Cellular telephone systems and wireless local loop systems incorporate a method of power control to minimize subscriber transmitted power. The power control system maintains each subscriber at threshold. In addition, both cellular telephone systems and wireless local loop systems do not re-use the same frequency at a base station. This does not eliminate the interference problems associated with systems like that in the Langston application that reuse frequencies at a base station to maximize capacity.
Other fixed wireless systems are known to use a measurement of signal to noise ratio to perform power control. The disadvantage of using signal to noise as a criteria for power control is that the power setting at the subscriber is performed on system interference as well as receiver noise. This is because the signal to noise measurement includes interference and actually measures signal to noise plus interference ratio. If subscriber power is increased when high interference is measured, the result is a further increase in interference.
The interference increase caused by increasing subscriber power may occur elsewhere in the system on a common frequency channel (frequency reuse between sectors and between nodes) and would be difficult to detect. It could further cause an increase in subscriber power elsewhere in the system resulting in or snowball effect, or system instability.